1. Field of the Invention
The present invention relates to an apparatus for performing heat treatment on a large-sized substrate and a heat treatment method with the use of the apparatus.
In this specification, a semiconductor device means all types of devices which can function by utilizing semiconductor characteristics, and an electro-optical device such as a liquid crystal display device and a light-emitting device, a semiconductor circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
In recent years, a technique for forming a transistor using a semiconductor thin film (with a thickness of several to several hundreds of nanometers) has attracted attention. Transistors are widely applied to electronic devices such as an IC and an electro-optical device, and are actively put into production as a switching element for an image display device.
Such a device described above is formed over a large-sized substrate so that a number of panels can be obtained from one substrate. However, in the case of using a glass substrate, there is restriction such that steps which are required to be performed at a temperature higher than or equal to the allowable temperature limit of glass can not be performed.
Therefore, when treatment at a high temperature for a long time is required, a laser annealing method, a rapid thermal annealing (RTA) method, or the like is used (patent document 1).
An RTA method is also referred to as RTP (Rapid Thermal Processing), in which an object to be heated can be rapidly heated and rapidly cooled using a heater or lamp light. Therefore, heat treatment can be performed at a temperature higher than or equal to allowable temperature limit of glass.
Further, because an RTA method does not require a complex optical system used for a laser annealing method, it is a suitable method for treating a comparatively large area uniformly.